US2311293A - Production of high concentrated fixing and hardening sirups - Google Patents

Description

Patented Feb. 16, 1943 PRODUCTION OF HIGH CONCENTRATED FIXING AND HARDENING SIRUPS Garnet Philip Ham, Old Greenwich, Com, assignor to American Cyanamid Company, New York, N. Y., a corporation of Maine No Drawing. Application November 30, 1940,

Serial No. 367,955

6 Claims.

This invention relates to the production of stock fixers and hardeners for silver halide photographic material.

In the past photographic fixing and hardening baths containing an alum as well as the soluble sodium thiosulfate and sulfite, were either prepared by dissolving the chemicals to form .a

. bath of normal concentration, usually about 250 grams of sodium thiosulfate to the liter, or the bath is made up in liquid form in which form it keeps for a reasonably long time. There has been a considerable demand for high strength sirups that could be diluted with water especially by users such as physicians and dentists who are not trained photographers and who wish to be able to fix their X-ray films with a minimum of time. Such high concentration sirups are of course of great advantage because it is possible to rapidly dilute them with water to the desired strength without dissolving any chemicals or without having to store relatively large volumes of normal strength fixing baths.

If it is attempted to prepare high concentration sirups using either sodium thiosuifate or preferably mixtures containing guanidine thiosulfate which show higher solubility, these sirups cannot be readily made by dissolving up the various ingredients in the normal manner. On the contrary, when it is attempted to make such sirups containing for example 1000-1200 grams of thiosulfate to the liter, precipitation takes place.

According to the present invention I have found that if the thiosulfate and part of the sullite are dissolved separately and the alum, acid,

and remainder of the sulflte dissolved in a separate solution, and then mixed, prefer-ably cold, no precipitation results and stable high concentration fixing sirups are obtained.

It is not desired to limit the present invention to any theory of action but it is my opinion that probably a factor of importance lies in the avoidance of excessive local concentrations where some of the solid materials are dissolving. The two solutions mix rapidly and completely and excessive concentrations in isolated zones are not obtained. It is of course possible that other factors may be present and may even be of greater importance.

Excellent sirups can be prepared as described above, but when guanidine thiosulfate mixtures are prepared by using the portions of guanidine nitrate with sodium thiosulfate, the sirups are sometimes not completely clear although usable. If, however, they are filtered through unactivated wood charcoal; they are completely clear and show excellent stability. I do not wish to lim this feature of the invention to. any particular theory but I am of the opinion that an important factor lies in small amounts of impurities which are usually associated with technical guanidine nitrate and which are probably adsorbed or removed by the charcoal filtration. When perfectly chemically pure guanidine nitrate is employed, the filtration is not normally required. This feature, while not an essential to the invention is of large practical importance as it permits the use of technical guanidine nitrate with a corresponding very marked saving in cost and therefore forms part of the preferred embodiment of the present invention.

By means of the present invention it is possible to obtainfixing sirups containing guanidine thiosulfate up to about 1000-1200 grams of thiosulfate per liter. Higher concentrations may be produced by the incorporation of hydrotropic materials such as urea. In the present case I do not claim the addition of hydrotropes generally as this forms the subject matter of the copending patent of Ham and Barnes No. 2,248,905, issued July 8, 1941.

The invention will be described in. conjunction with the following specific examples.

EXAMPLE 1 Two solutions were prepared as follows:

Solution A Parts Water 700 Sodium sulfite (anhydrous) 30 Sodium thiosulfate (5H2O) 1000 Guanidine nitrate 208 Solution B Parts Water 300 Acetic acid (28%) 200 Boric acid 30 Potassium aluminum sulfate 60 Sodium sulfite 32 portrait film in approximately 2 minutes and X-ray film in about 1 /4 minutes. The sirup shows excellent stability and at room temperature does not show any precipitation after 30 days. At higher temperatures, however, about 49 C., considerable suliurization results after about six days.

When the same materials are used but the solids dissolved in the order-sodium sulfite, guanidine nitrate, sodium thiosuliate, acetic acid, boric acid, potassium aluminum sulfatea heavy precipitation was formed containing precipitate showing sulfur and an-aluminum complex. Even after filtering a precipitate reappears.

Higher stability especially at high tempera tures may be obtained by incorporating 36 parts of urea in solution A before filtering through charcoal. This sirup is not only completely stable at room temperature but also at 6 C. and 49 C. respectively. Difliculty is encountered even with the powerful hydrotropic substance, urea, if the ingredients are dissolved one after the other without preparing the two separate solutions. Other hydrotropes such as those described in the Ham and Barnes patent above referred to, may be substituted for the urea.

A concentrated fixer and hardener sirup was prepared by forming the following two solutions:

Solution A Parts Water 350 Sodium thiosulfate (H:O) 600 Sodium sulfite (anhydrous) 15 Solution B Parts Water 150 Acetic acid (28%) 100 Boric acid 15 Potassium aluminum sulfate 30 Sodium sulflte (anhydrous) 16 The solutions were mixed together,

through unactivated charcoal as described in the preceding example, and gave a satisfactory fixing and hardening solution when diluted with water. In the above examples potassium alum is used and in a similar manner chrome alum may be employed although the stability of the re sulting solution is not quite as high. a

What I claim is:

1. A method of preparing a high concentration stable fixing and hardening solution for silver halide photographic material containing a soluble thiosuliate in amounts of the order of magnitude of 1000 to 1200 grams per liter. sulfite, and alum hardener which comprises dissolving in water the desired amount of soluble thiosul fate and at least a considerable portion 01' the sulfite, separately dissolving in water the alum hardening ingredients under acid conditions, and mixing the two solutions together.

2. A method of preparing a high concentration stable fixing and hardening solution for silver halide photographic material containing a soluble thiosuli'ate in amounts of the order of magnitude of 1000 to 1200 grams per liter including guanidine thiosuli'ate in effective amounts, sulfite, and alum hardener which comprises dissolving in water the desired amount of solublethiosuli'ate and at least a considerable portion 01' the sultite, separately dissolving in water the alum hardening ingredients under acid condi tions, and mixing the two solutions together.

3. A method according to claim 1in which a hydrotropic substance is incorporated in the first solution.

4. A method according to claim 2 in which a hydrotropic substance is incorporated in the first solution.

5. A method according to claim 1 in which urea is incorporated in amounts sufiicient to exert a hydrotropic action onvthe thiosuliate.

6. A method according to claim 2 in which urea is incorporated in amounts sufiicient to exert a hydrotropic action on the thiosuii'ate.

GARNET PHHJP HAM.